Function encrypt_xaes256_gcm 

pub(crate) fn encrypt_xaes256_gcm(
    plaintext: &[u8],
    key: &XAes256GcmKey,
    content_format: ContentFormat,
) -> Result<CoseEncrypt0Bytes, CryptoError>

Encrypts plaintext with XAES-256-GCM and returns a typed COSE Encrypt0 message.